Apparatus for stretching webs



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APPARATUS FOR STRETCHING WEBS Filed March 24, 1952 5 Sheets-Sheet 3INVENTOR.

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United States Patent APPARATUS FOR STRETCHING WEBS Donald F. Miller,Bloomingdale, N. 1., assignor to E. L du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware Application March 24, 1952,Serial No. 278,252

7 Claims. (Cl. 26-57) This invention relates to an apparatus forstretching webs and more particularly webs of sheet materials. Stillmore particularly it relates to an apparatus for simultaneouslystretching webs in a lateral and longitudinal direction.

An object of this invention is to provide an improved apparatus forstretching webs. A further object is to produce such apparatus which issimple in construction and effective in operation. A still furtherobject is to provide such apparatus wherein the degree of lateral andlongitudinal stretching can be regulated in a simple manner. Still otherobjects will be apparent from the following specification.

The apparatus of this invention will now be described with reference tothe accompanying drawings which form a part of this specification. Inthe drawings which illustrate practical embodiments of the invention,

Fig. 1 is a top plan view of a stretching apparatus embodying theinvention,

Fig. 2 is a perspective view in a larger scale of a portion of theadjustable stretching unit showing the cam track, chain links and agripper,

Fig. 3 is a section taken along the line 3-3 of Fig. 1 showing the chainlinks, gripper and web,

Fig. 4 is a perspective view of a link structure,

Fig. 5 is a perspective view of an alternative link structure,

Fig. 6 is a plan view of a chain with four links in stackedrelationship,

Fig. 7 is a section of the upper part of a chain with four links instacked relationship,

Fig. 8 is an elevation of part of a chain with three links in stackedrelationship,

Fig. 9 is a plan view of a chain link with a curved slot in closedposition,

Fig. 10 is a plan view of a chain link with a curved slot in an extendedposition,

Fig. 11 is a schematic view of two links with the cam surface oppositefrom the direction of travel,

Fig. 12 is a schematic view of two links with the cam surface in thesame direction of travel,

Fig. 13 is a plan view of a series of grippers mounted on chain pins,and

Fig. 14 is a sectional view taken along the line BB of Fig. 13.

Referring now to Fig. 1, bedplates 1 and 2 are pivotally mounted on asuitable frame 3 shown in dotted outline by means of pivot pin 4 whichinterfits with a hole 5 on the lateral lug extension 6 of bedplate 2.The pin is fixed to lug extension 7 on bedplate 1. The bedplates rest onthe frame member and their position with respect to each other and axisA-A can be regulated by means of lead screw 8 that is journaled inbearing 9 which is pivotally mounted on plate 2 as schematically shownin Fig. 1 with the pivot 9' in dotted outline, said bearing beingthreadably engaged with the upstanding lug 10 which is similarlypivotally mounted on bedplate 1 with the pivot 10 being shown in dottedoutline. The upper Patented July 24, 1956 and lower blocks of thebearing and lugs are held together by means of screws 43. Screw 8 isfastened suitably at its journaled end so that it will turn freely butcannot move along its axis. The other end of the screw is provided witha handle 11 so that it can be turned. When thehandle is turned in onedirection the bedplates are drawn closer together and when turned in theopposite direction spread farther apart. This adjustment determines thedegree of lateral stretchinggiven to web W (e. g., a transparentnon-oriented polymer).

While the bedplates are shown as being pivoted on a common pin thisconstruction, while simple and practical, is not essential as the platescan be pivoted separately or provided with lead screws and threaded lugsso that each end can be adjusted and admit of the stretching of widerwebs. Various modifications can be made to permit angular displacementof the plates from a common axis.

The degree of longitudinal stretching is determined by the variablepitch stretcher chains 12. They are identical in construction but travelin opposite directions. The stretcher chains consist of a series ofidentical links. Each link consists of a flat L-shaped link body member14 which is provided with a pivot hole 15, which, as shown in Figs. 2and 4 consists of a round hole. Spaced from this hole is an elongatedslot 16 that can be straight or curved. The curved tip 17; whichconstitutes an extension of the cam surface side of the L-shaped linkbody, coacts with a cam track and this is explained further below. Theend of the slot nearest the pivot hole preferably is formed in ahalf-round. The chains are not shown as a complete unit in any view, forthe sake of clarity. However, the pivot pins, which as shown are fittedinto the pivot holes by a close fit, indicate the positions therespective chains take when in assembled relationship.

The chains can be operated in either direction depending upon whether astretching or controlled shrinking operation is being carried out, asdescribed below.

In the link of Fig. 4, the axis of the slot is at an angle greater thanfrom said longitudinal axis. This angle determines the force F tendingto rotate the link around its axis. The pitch of the chain and thedegree of longitudinal stretching can be varied in the case of thespecific shape of link of Fig. 4 from x to nx. In the link of Fig. 4pivot hole 15 is in the outer, upper part of the toe and the slot 16extends along the base of the L-shaped link. The side and top of thislink form a contacting surface to engage with a cam track whichregulates the rate and extent of their pivoting and the consequentdistance between the centers of the adjacent pins. This, in turn,regulates the rate and extent of longitudinal stretching of the web.

A variable pitch chain 12 which is illustrated in Fig. 1 with only twooverlapping links being shown in three spaced positions, in order toavoid confusion, is made by joining two sets of alternate pairs of linksby means of pins 18 which pass through the pivot hole 15 of one link andthe elongated slot 16 of the next link in the chain. These links arestacked alternately above and below each other as shown in Figs. 1 and 2and when all links are present form a closed chain. Two sets of linksare shown in these figures and they are spaced a short distance apart byintervening guide members. Thus, as shown in Fig. 2 they are separatedby guide plate 35. The round surfaces of pins 18 between the two setsmesh with a driving sprocket 19 and idler sprocket 20. The

teeth on the driving sprocket are spaced to have a pitch equal todistance nx so that it will mesh with the pins when the links are attheir maximum extended position. The teeth on the idler sprocket are sospaced that the pitch is equal to distance x. This means that the links3 are at closed position as they enter stretching units 13.

The path of pins 18 between idler sprocket 20 and the guide roller 21 isessentially a straight line. The closed chain 12 passes around drivingsprocket 19 which is spaced above and to one side of guide roller 21 andreturns to idler sprocket 20 forming a triangular shaped path. Thesprockets and roller may be journaled on stub shafts suitably mounted onthe bedplates. The links in the chain on bedplate 1 are reversed withrespect to those on bedplate 2.

The upper end of each pin or alternate pins or regularly spaced pins isextended as shown in Figs. 2 and 3 through and fixed to an L-shapedbracket 22 which has a gripper arm 23 pivoted in a slot 24 in one arm ofthe bracket. The other arm of the L-shaped bracket is forked and has anopen-ended slot 26 which engages with adjacent chain pin 18. Thisstructure keeps the grippers in proper alignment during the stretchingoperation. The pivot pin may be fixed to the bracket on opposite sidesof the gripper arm or fixed to the gripper arm and journaled in thebracket on each side of the slot. The chain pin also extends through agripper base plate 27 which extends below the projection of the bracketand under the gripper arm. This plate serves as a rest for the selvageof web W. It may be integral with the bracket body 22 or welded orotherwise affixed thereto, e. g., by means of pins 28. This form ofgripper is common in ten-tel frames. When tension is applied to stretchthe web, the gripper arm pivots to grip the web more tightly. Only onegripper is shown in Fig. 2 for the sake of clarity. They may be disposedon each pin 18 as shown in Figs. 13 and 14.

Bedplates 1 and 2 are provided with guide rails 29. They may be castintegrally with the bedplates or may be welded, bolted or otherwiseafiixed to the latter. The inside surface of the rails is substantiallyparallel to the locus of the pins as they pass from the idler sprocketto the driving spocket. Second guiding rails 30 are also mounted on thebedplates. They are pivoted at their respective lower end on pivot pin31. The opposite ends of the guide rails have the end of a screw 32attached thereto. Each screw is threada-bly engaged with an upstandinglug 33 on the respective bedplate. The outer end of the screws areprovided with turning handle 34. As shown the guide rail 39 is in theform of a U-s'haped channel. A central plate 35 extends from eachchannel, its upper and lower surfaces act as bearing surfaces for theItlat portion of the inner links. The outer edge of each central plateis disposed parallel with the inner edge of guide rail 2? when ininnermost position and the distance between these edges when in suchposition is slightly greater than the diameter of pins 18. The inneredge of the U-shaped channel slants with respect to the edges of theguide rails and forms a slanting cam track 36 which engages with theedge and end of each L-shaped link. By adjusting the U-shaped channelsby means of screws 32 one can regulate the distance between each twoadjacent pins as one of the pins of each pair slides in elongated slots16. The degree of slant of :the U- shaped guide rail can *be regulatedso that the amountof longitudinal stretch of the web can be varied fromx to ms. In general, the degree is adjusted'sothat the distance does notincrease to the full amount nx.

Tripper arms 37 are placed in the path of the gripper arms at or nearthe end of guide rails '29 to disengage-the grippers. A part of thetrippe-r arm is also shown in Fig. 2 and this part forms a cam surfacewhich lifts each gripper arm and removes it from contact with the web asthe chain moves past the gripper release station.

As the links pass from the cam track due to tension on the chains andthe fact that the teeth of driving sprocket 19 are spaced at maximumpitch the pins 18 extend apart to their permitted maximum distance.

Link-rcaligning unit 3 8 is placed in the path of the pins between thedriving and driven sprockets and preferably near the latter in order toassist in bringing the links into alignment before they pass into thestretching unit or zone. These units may have a construction similar tounits 13 and be composed of a channel member 4% and rails 39 and 41 andsimilar to members 29, 30 and 35 so that they not only realign the linksbut tighten the chain. The rails 39 can be afiixed to the respectivebcdplates in any suitable manner, a. g., by welding, screws, bolts, etc,and rails 41 can be made adjustable like members 23 by means of leadscrews, etc. While a space has been shown between the end of members 39and 40 of unit 38 and minimum pitch sprocket 20 for the sake of clarity,in actual construction members 39 and 40 can be extended so as to form aguiding surface right up to the point where the link pins contact withthe sprocket teeth. Similarly, members 29 and 30 of unit 13 can beextended to the point where the link pins contact with the sprocketteeth 19. Thus the upper portions of the guide members may overlap thefiat surfaces of the sprockets. A curved cam 42 is provided about eachsprocket to open the grippers and allow them to close and grip the web Was it passes into the path of the grippers.

In Fig. 2 the links 18 are stacked pairs thus providing a relativelysmooth surface to engage with the horizontal surfaces of the track inthe stretching unit. The contour of the links can he modified so thatthey can be stacked in units of 3 or 4 or even more. Further, it is notnecessary that each pin be connected to the adjacent links through thepivot hole of one and the elongated slot of the next link. Thus, inFigs. 6 and 7, a four-link stacking arrangement is shown where alternatepairs are spaced. Theyv are shown in solid elevation for clarity.

Fig. 8 illlustrates a three-link stacking arrangement in section and isself-explanatory.

Figs, 9, 10, 11, and 12 require no extended description since theirfunction is clear from the above. It will be noted, however, that theangle 0 remains :the same regardless of the amount the link has rotatedand the chain thereby extended. The force tending to rotate the linktherefore will remain constant. In the link shown in Fig. 5 the angle 6increases with the rotation of the link as does the rotating force.

Figs. 11 and 12 merely illustrate that the chain links can be reversedand still function the same when the chain travels in the samedirection. As stated above the chain may travel in either direction.

In Figs. 13 and 14 there is illustrated a series of grippers mounted onsuccessive pins 18. The plates of these grippers have been eliminatedfor the sake of clarity. The chain links have not been shown for asimilar reason. However, the assembly on a pin is shown in Figs. 2 and3.

In place of the pivoted arms 23 which have a rounded bottom there may besubstituted pivoted arms with an elongated flat plate which is providedwith pins to pierce the web to be stretched. This type of gripper isillustrated in U. S. Patent 650,385 to Gadd.

While the sprocket of minimum pitch has been described as a drivensprocket it maybe connected by .a suitable chain or series of gears tothe same source of power that turns the driving sprocket of maximumpitch.

The contour of the links can vary considerably so long as there is apivot point and .a slot which allow the pins to separate. Thus, in thealternate form of construction shown in Fig. 5., the pivot hole andadjacent end of the slanting slot are near the heel of the L-shaped linkand the pivot hole is nearest the base. Obviously, still otherconfigurations can be used. The links need not be L-shaped but may beoval, e.tc. preferably with cut-away portions if necessary so that themay close to minimum pitchand expand to maximum .pitch withoutinterference with the pins.

Various heating and cooling devices, e. ;g,., 13 195, Coils, jackets,etc, can be provided along the web travel to control the operations.Thus, the grippers can be heated or cooled. Various other types ofgrippers can be substituted for those shown and described above.

The operation of the apparatus will now be explained with reference tothe stretching of a non-oriented superpolymer film, e. g., polyethyleneterephthalate films of the type described in Whinfield et al., U. S.Patent 2,465,319. A web W of non-oriented or non-stretched polyethyhleneterephthalate film uncoated or coated with a vinylidene chloridecopolymer layer of the kind described in Alles and Saner, U. S. app.Ser. No. 151,274, filed March 27, 1950, now U. S. Patent 2,627,088, andin Pitzel U. S. Patent 2,570,478 is fed directly from an extrusiondevice or from a supply roll (none being shown) into the stretchingapparatus. The lower surfaces of the respective edges of the web aredirected onto gripper base plates 27 and gripper arms fall by gravityinto contact with the upper surface of the web. As the web passesthrough the stretching device to a windup station or other apparatus(not shown) tension is gradually applied laterally and longitudinallybecause of the divergency of the bedplates and because the links areactuated and pivot so that the pitch (i. e., distance between successivepins 18) increases from minimum to a greater pitch determined by theamount of stretching it is desired to effect in tthe web. The grippersare released after the maximum desired stretch has been accomplished.The web then passes on for any desired further treatment.

Instead of relying upon gravity to actuate the gripper arms they may beactuated by a cam surface or tripping device similar to that describedabove for releasing the gripper arms but in reverse direction.

It should be apparent to those skilled in the art that the invention isnot limited to the stretching of polyethylene terephthalate film but maybe used in stretching webs of many diverse types including not onlyresins and superpolymers, e. g., nylon, polyethylene, polyvinylchloride, poly(vinyl chloride co vinyl acetate); cellulose derivatives,e. g., cellulose acetate, cellulose formate, cellulose propionate,cellulose acetate-butyrate; methyl, ethyl, butyl, benzyl, allyl andcrotyl celluloses; rubber hydrochloride, and polystyrene, but fabricsmade of wool, silk, cotton, cellulose acetate, viscose rayon, nylon,etc., metal foils, e. g., lead, aluminum, etc., can be stretched in asimilar manner.

The apparatus is not limited to stretching so that a permanent set isobtained as it may be used to make elastic fabrics by suitabletechniques along the selvage, etc., during travel of the web. It isuseful for controlled shrinking of fabrics in which case it would beoperated in reverse.

While the apparatus is primarily designed for stretching in twodirections, it is not limited to that treatment. Thus, by adjusting thebedplates so that the path of the pins is parallel to the sides of theweb, longitudinal stretching only can be accomplished.

As many widely different embodiments of this invention can be madewithout departing from the spirit and scope thereof, it is to beunderstood that the invention is not to be limited except as defined bythe claims.

What is claimed is:

l. A web-stretching apparatus comprising a pair of bedplates which arecapable of being separated in essentially the same plane from a commonperpendicular axis, a sprocket of minimum chain pitch, a guide rollerand a sprocket of maximum chain pitch, each revolubly mounted on oneonly of each bedplate to form a circuitous path for a chain capable ofextending and contracting between maximum and minimum pitch, each chainbeing composed of regularly spaced pins which mesh with said sprocketsand extend through two separated rows of links, each link having a pivothole and an elongated slot extending through from the top to the bottomsurfaces of its flat body, the locus of the center of the slot beingoffset from the pivot hole, each link being joined in chain fashion sothat adjacent pins pass through the pivot hole of one link and elongatedslot of another, adjustable guide rails on each bedplate between theguide roller and sprocket of minimum chain pitch to form a path for thechain pins and links, one of said rails being provided with a slantingcam surface on which the edges of the links ride to control the degreeof pivot and the distance the links are extended, web grippers mountedon regularly spaced pins, means to actuate said grippers to grip theWeb, means to release the grippers and guide rails to realign the links.

2. A web stretching apparatus comprising a pair of flat bedplates whichare capable of being separated in essentially the same plane from acommon perpendicularaxis, a driven sprocket of minimum chain pitch, aguide roller and a driving sprocket of maximum chain pitch, eachrevolubly mounted on one only of each bedplate to form a circuitous pathfor a chain capable of extending and contracting between maximum andminimum pitch, each chain being composed of regularly spaced pins whichmesh with said sprockets and extend through two separated rows of links,each link having a pivot hole and an elongated slot extending throughfrom the top to the bottom surfaces of its flat body, the central axisof the slot being offset from the pivot hole and its ends being ofunequal distance from the pivot hole, each link being joined in chainfashion so that adjacent pins pass through the pivot hole of one linkand elongated slot of another, adjustable guide rails on each bedplatebetween the guide roller and driven sprocket to form a path for thechain pins and links, one of said rails being adjustable and providedwith a slanting cam surface on which the edges of the links ride tocontrol the degree of pivot and the distance the links are extended andthe other forming a straight path parallel to the tangent between saidminimum chain pitch sprocket and said guide roller, Web grippers mountedon regularly spaced pins, means to actuate said grippers to grip theweb, means to release the grippers and guide rails between the drivingsprocket and driven sprocket, one of such rails being adjustable and theother forming a straight path parallel to the tangent between saidsprockets to realign the links.

3. A web-stretching apparatus comprising a pair of bedplates which arepivoted near one end and capable of lateral separation in essentiallythe same plane from a common perpendicular axis at the other end, adriven sprocket of minimum chain pitch located near the pivoted end ofthe bedplate and spaced laterally from said axis, a guide roller spacedlongitudinally from said sprocket and laterally from said axis and adriving sprocket of maximum chain pitch spaced a greater lateraldistance from said axis on each bedplate to form a triangular path for achain capable of extending and contracting between maximum and minimumpitch, each chain being composed of regularly spaced pins which meshwith said sprockets and extend through two separated rows of extensiblelinks, each link having a pivot hole and an elongated slot extendingthrough from the top to the bottom surfaces of its flat body, thecentral axis of the slot being offset from the pivot hole and its endsbeing of unequal distance from the pivot hole, each link being joined inchain fashion so that adjacent pins pass through the pivot hole of onelink and elongated slot of another, adjustable guide rails on eachbedplate between the guide roller and driven sprocket to form a path forthe chain pins and links, one of said rails being adjustable andprovided with a slanting cam surface on which the edges of the linksride to control the degree of pivot and the distance the links areextended, web grippers mounted on regularly spaced pins said grippershaving an arm with an elongated slot which engages the pivot pin of anadjacent gripper, means to actuate said grippers to grip the web, meansto release the grippers and guide rails between the driving sprocket anddriven sprocket, one of such rails being adjustable and th other forminga stra ght p th p ra le o he ansen e w n s i spro ket to re lign th link4. An apparatus as set forth in Claim 3 wherein the links in each roware stacked in units of three, one of each two adjacent pins extendingthrough the pivot hole of one link and the slot of the next one but thelinks overlapping in units of three one above the other and the next twooverlapping but underneath the top and next link.

5. An apparatus as set forth in claim 3 wherein the links in each roware stacked in units of four With alternate pairs being adjacent to eachother and two adjacent pins extending through the pivot hole and slot ofadjacent links.

6. A web-stretching apparatus comprising a pair of flat bedplates whichare pivoted on a common perpendicular axis near one end and are capableof lateral separation in essentially the same plane from a common axisat the other end, means for adjusting the lateral separation of saidhedplates, a driven sprocket of minirnumchain pitch located near thepivoted end of the bedplate and spaced laterally from said axis, a guideroller spaced longitudinally from said sprocket and laterally from saidaxis and a driving sprocket of maximum chain pitch spaced a greaterlateral distance from said axis on each bedplate to form a triangularpath for a chain capable of extending and contracting between maximumand minimum pitch, each chain being composed of regularly spaced pinswhich mesh with said sprockets and extend through two separated rows oflinks, each link having a pivot hole and a curved elongated slotextending through from the top to the hottom surfaces of its flat body,the locus of the center of the slot being offset from the pivot hole andits ends being of unequal distance from the pivot hole, each link b eingjoined in chain fashion so that adjacent pins pass through the pivothole of one link and elongated slot of another, adjustable guide railson each bedplate between the guide roller and -driven sprocket to formstraight paths for the chain pins and links, one of said rails beingadlustahle to provide a slanting cam surface on which the edges of thelinks ride to control the degree of pivot and the distance the links areextended and the other forming a straight path parallel to the tangentbetween said minimum pitch sprocket and said guide roller, web grippersmounted on regularly spaced pins, means to actuate said grippers to gripthe web, means to release the grippers and guide rails betweenthedriving sprocket and driven sprocket one of such rails being adjustableand the other forming a straight path parallel to the tangent betweensaid sprockets-to realign the links and grippers.

7. An apparatus as set forth in claim 6 wherein the links in each rowoverlap one above the next in order, so that each adjacent pin extendsthrough the pivot hole of one link and the slot of the next.

References Gited in the tile of this patent UN TED STA ES ATEN

1. A WEB-STRETCHING APPARATUS COMPRISING A PAIR OF BEDPLATES WHICH ARECAPABLE OF BEING SEPARATED IN ESSENTIALLY THE SAME PLANE FROM A COMMONPERPENDICULAR AXIS, A SPROCKER OF MINIMUM CHAIN PITCH, A GUIDE ROLLERAND A SPROCKET OF MAXIMUM CHAIN PITCH, EACH REVOLUBLY MOUNTED ON ONEONLY OF EACH BEDPLATE TO FORM A CIRCUITOUS PATH FOR A CHAIN CAPABLE OFEXTENDING AND CONTRACTING BETWEEN MAXIMUM AND MINIMUM PITCH, EACH CHAINBEING COMPOSED OF REGULARLY SPACED PINS WHICH MESH WITH SAID SPROCKETSAND EXTEND THROUGH TWO SEPARATED ROWS OF LINKS, EACH LINK HAVING A PIVOTHOLE AND AN ELONGATED SLOT EXTENDING THROUGH FROM THE TOP TO THE BOTTOMSURFACES OF ITS FLAT BODY, THE LOCUS OF THE CENTER OF THE SLOT BEINGOFFSET FROM THE PIVOT HOLE, EACH LINK BEING JOINTED IN CHAIN FASHION SOTHAT ADJACENT PINS PASS THROUGH THE PIVOT HOLE OF ONE LINK AND ELONGATEDSLOT OF ANOTHER, ADJUSTABLE GUIDE RAILS ON EACH BEDPLATE BETWEEN THEGUIDE ROLLER AND SPROCKET OF MINIMUM CHAIN PITCH TO FORM A PATH FOR THECHAIN PINS AND LINKS, ONE OF SAID RAILS BEING PROVIDED WITH A SLANTINGCAM SURFACE ON WHICH THE EDGES OF THE LINKS RIDE TO CONTROL THE DEGREEOF PIVOT AND THE DISTANCE THE LINKS ARE EXTENDED, WEB GRIPPERS MOUNTEDON REGULARLY SPACED PINS, MEANS TO ACTUATE SAID GRIPPERS TO GRIP THEWEB, MEANS TO RELEASE THE GRIPPERS AND GUIDE RAILS TO REALIGN THE LINKS.